Inclined-piston dead-weight pressure gauge



July 12, 1966 D. R. DoUsLlN INCLINED-PISTON DEAD-WEIGHT PRESSURE GAUGEOriginal Filed Feb. 28 1963 5 Sheets-Sheet 1 R 8 m m m m 5 ,n V W W. w MQ A w R. l Jr w @Pi mm M 1M QQ m y my um \m mM (S mm mw a i A W Z NINNIH di! mv IHH \mm rm B .|||x.|| n@ 1.@11' il .MMUlixllml IMM@ I 1 1 nwlulrhll. mm um q mm\ Il Q @NM /Q.` w N um ,M/ N mw\ hv n r WN .2 l QM f/V/vl f 1 l July 12, 1966 D. R. DoUsLlN INGLINED-PISTON DEAD-WEIGHTPRESSURE GAUGE Original Filed Feb. 28, 1963 :5 Sheets-Sheet 2 II ||Y|| IN @TA @im um mm uw mm w mm uw i w- W S v/ WS mm mv N G`l kb hm. mm bm.

v/Il INVENTOR DONALD DOIJSL/N 'nl J July 12, 1966 D. R. DoUsLlNINCLINED-PISTON DEAD-WEIGHT PRESSURE GAUGE Original Filed Feb. 28. 1965:3 Sheets-Sheet 5 INVENTOR VLD R. @0l/5L IN BY AzLoRNEi/s United StatesPatent O 3,260,118 INCLINED-PISTON DEAD-WEIGHT PRESSURE GAUGE Donald R.Douslin, Bartlesville, Okla., assigner to the United States of Americaas represented by the Secretary of the Interior Original applicationFeb. 28, 1963, Ser. No. 261,913, now Patent No. 3,195,354, dated July20, 1965. Divided and this application Apr. 21, 1965, Ser. No. 469,357Claims. (Cl. 73-419) The invention herein described and claimed may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of royaltiesthereon or therefor.

This is a division of application Serial No. 261,913, tiled February 28,1963, now Patent No. 3,195,354.

This invention relates to a dead weight pressure gauging apparatushaving controls for producing a zero pressure differential, or a nulleffect upon a tiltable piston operably supported to move freely in theapparatus. More particularly, the invention concerns improvements in asensitive pressure gauge in which a component force created by the deadweight of a piston structure brought to an angular displacement from thehorizontal, is applied to counterbalance a force on the piston exertedby the pressure of a substance under test. This improved pressure gaugemay be adapted to provide very accurate vapor pressure data, and can beemployed to very good advantage for measuring the vapor pressure ofsubstances whose volatility range is such that it becomes impractical touse ordinary ebulliomfetric or static vapor pressure apparatus. Accuratevapor pressure data on volatile substances such as hydrocarbon, sulfurand nitrogen compounds is obtained without difiiculty by means of thegauge according to the present invention. Measurements in the pressurerange from 0.1 to 40 mm. Hg are attainable even though small samples ofsuch substances are used. The gauge is also applicable to provideprecise data on gas pressures other than vapor pressures.

Since the accuracy of the gauge is dependent upon establishing withinclose limits the magnitudes of the forces acting on a piston, thepresent invention comprises means to substantially eliminate therelatively significant indeterminate forces of friction to which thepiston might be subject. Provided for the purpose is a uniquebi-directional drive which is transmitted to the piston for irnpartingthereto an oscillatory motion without producing any susceptible endthrust to act axially upon the piston.

An object of the present invention therefore is to provide a deadweightpressure gauge comprising an angularly adjustable arrangement in which aweighted element is displaced to counterbalan-ce the force of thepressure applied to be gauged.

A further object of the present invention is to provide a preciselyaccurate pressure gauge apparatus comprising an arrangement ofcylindrical elements including a piston driven for rotational anddirectional displacements therein, on which frictional forces of therotation are effectively eliminated, and other forces are adjusted to acounterbalance effectuating a null condition in the piston drive for adirectional displacement.

These and other objects and advantages of the invention will be moreclearly understood from the following description of a preferredembodiment of the invention, considered together with the accompanyingdrawing wherein:

FIG. 1 is a sectional view through a main housing of the invention,showing in detail the elements of the piston-cylinder structure madeoperable therein;

FIG. 2 is a sectional view taken partly on line 2 2 3,260,118 PatentedJuly 12, 1966 of FIG. 1, and showing the details of a rotatableauxiliary housing and its support, to which the housing of FIG. 1 isjoined and made operable thereby for tilting in a vertical plane; and

FIG. 3 is a schematic diagram illustrating various parts of theinvention including the piston-cylinder structure of the gauge, as theseparts ar-e arranged when applied in a pressure measuring operation.

A pressure sensing and indicating apparatus according to the presentinvention, is shown lin FIGS. 1 and 2, to comprise at its core, a hollowcylindrical piston 10 supported for displacement within a piston housingcylinder 12. This combination of parts is in turn supported fordisplacement within a tubular housing or enclosure 15. Comprising thetubular enclosure are an elongated cylindrical sleeve 16, havingexternally threaded portions adjacent each of its open ends 17 and 18.Closure caps 19 and 20 having screw threads suitably arranged therein,fasten over the open ends 17 and 18, respectively of the sleeve 16,whereon the caps are positionable to bring together the structuralelements assembled within the tubular enclosure 15, in a manner to behereinafter more fully explained.

Arranged from right to left between the closure caps of the housing 15,along the longitudinal axis A-A thereof as viewed in FIG. l, are aseries of contiguous interspaces, or chamber-like sections 22, 23, 24and 25, in which are located the several operatively related integratedparts of the structure arranged within the cylindrical sleeve 16.Enclosed within the relatively long intermediate space 24 of the sleeve,is the structure comprising piston 1t) and cylinder 12, constituting theprincipal operative component of the apparatus. Within the slightlywider cylindrical space 25 of the sleeve is enclosed a ring-like wormgear 27, and a thrust ball bearing element 29. One race of the bearingelement is brought to bear upon the narrow web of gear 27, which itselfis attached to the surface defining one end rim of th-e cylinder 12, bylong screws or the like, whereby a wide opening in the gear conforms tothe opening in the end of the cylinder. In this manner cylinder 12 isfixed to rotate with the gear 27 when the gear is driven by a worm 75made operative by means to be hereinafter more fully described. Aninternally threaded portion of sleeve 16 located within section 25,receives in engagement therewith a bearing retainer member 30. Composingthis member is a thick ange from which projects a central con duit 31.On a shoulder formed by the cylindrical surface of conduit 31, and theliange, is situated the matching race comprising ball bearing 29. Formedas an integral part of the conduit 31 to cover over its extended end, isan apertured wall 32 comprising a number of small openings 33. A pointedprojection 34 at the center of the wall 32, is adapted to stop piston 10at one limit of its longitudinal displacement in the cylinder 12.

Arranged in a substantially similar manner in section 23 of the sleeve,are elements analogous to those in section 25. Included is a thrust ballbearing 36, having parts including one race, fastened to the rim surfaceat the other end of cylinder 12, and parts including the matching race,maintained on a shoulder formed on a second bearing retainer member 35.Like itscounterpart in section 25, the retainer member 35 comprises arelatively thick flange having threads thereon and a conduit portion 37.However, conduit 37 is fully open at both ends, and receivestherethrough as elongated tubular element 38 4in whose surface asubstantial number of evenly spaced holes have been made, to lighten it.The greater part of tubular element 38 is tightly fitted Within thecavity formed by the shell of piston 10, whereby f the element ispositioned to extend out into the relatively wide section 22, of sleeve16. In the open end of the tubular element 38 located within the piston1t), is secured a di-sk-like plug 46, to whose center is fastened a slimshaft 47, passing axially through the element and extending slightlyoutside the opposite end opening thereof. Shaft 47 is adapated to bereceived through an axial passage in a weight 48 made of iridium orgold, whereon the weight is retained in contact with the plug 46 bymeans of an elongated ared expansion lsleeve or other suitable fasteningfitted to the shaft 47. A thin disk 39 having a central opening, isconcentrically arranged and fastened on the rim defining the opening atthe opposite or extended end of tubular element 38. At the outerperiphery of disk 39, which closely conforms to the internal diameter ofsecti-on 22, there is attached by screw or the like, a small weight 4t),formed as a peripheral segment on the disk.

A short circular flange 41 protruding from the outer cylindrical surfaceof sleeve 16, forms a relatively wide opening 42 through which may beseen the various parts arranged within section 22. Across the inside endof opening 42 is located a scale or index 45. The thin edge of disk 39is movable along this index to indicate through opening 42 the relativelongitudinal position of the piston 10. Threads on the lip of flange 41,receive a cap 43, the head of which comprises a sight glass 44 allowingthe view of the disk and scale through opening 42, while maintaining asealed atmosphere in the chamber of sleeve section 22.

Elements of substantially identical form arranged within the respectiveclosure caps 19 and 20, facilitate a path for gaseous ilow out of andinto the housing 15. Associated with cap 19 for example is a relativelyshort conduit 50, provided with screw threads inside one end `adapted tohave joined thereto a conventional pipe nipple for coupling gas flowconduits to the apparatus. An end face 51 of a flanged portion at theother end of the conduit, is slightly reduced to dene a depressedperipheral surface. A narrow track formed in such peripheral surfacesecures a gasket 52 made of Teflon or the like, in position to effect asealing contact upon the surface of a 'raised ring following the rim of:an opening 17 in the sleeve 16, when the end surface 51 is received asa plug within the sleeve. Between the inner surface of cap 19 and theflange portion of the conduit 50, is a packing ring 53 maintaining theconduit and plug firmly is sealing contact when the cap 19 is drawn upon the exterior screw threads provided at the ends of the housingsleeve. The corresponding association of elements found between opening18 of the housing sleeve and the cap 20, include a conduit and plug 55having a gasket 56, and a packing ring 57 which like the ring 53, aidsin obtaining positive closure on the plug gasket when the gauge isassembled. The portions ofthe conduit plugs 50 and 55 extending outsideof the housing 15 are received through appropriately sized centralopenings in the respective closure caps.

Supporting housing for operational manipulation is an arrangement ofystructure best shown in FIG. 2, which enables a precise limitedrotative displacement of the housing about an axis transverse thereto,and multiple rotations of the piston and cylinder combination within thehousing about the longitudinal axis thereof. A fundamental component ofthe support structure is a further housing 60 whose outer form is` anintegral surface defined by a series of cylindrical portions ofgradually diminishing diameters. Cooperatively related within andwithout the cylindrical portion of the housing are the various elementalparts constituting the drives for causing the aforementioned rotationaldisplacements. Housing 60 is mintained in a operative position in astanchion comprising a leveling base 61, from which rise uprights 62 and63. At a suitable height above the base, the uprights 62 and 63 havealigned openings in which are secured flanged bearing sleeves 64 and 65,re-

spectively. Cylindrical portions 66 and 67, at spaced intervals alongthe housing 60, are received in the respective bearing sleeves 64 and65. A worm gear 68 is fixed to the housing 68 at one end of cylindricalportion 66, in contact with a spacer element 69 bearing on a rim ofbearing sleeve 64. Maintaining a worm 70 in operative relationship withworm gear 68, are a number of support bearings mounted in brackets suchas element 71, which are fastened at suitably spaced locations on theupright 62. Worm 78 can be made operative to drive the gear 68, by handactivated means or any power controlled gear drive arrangement.

To properly locate the worm gear 27 of housing 15, for an operativeconnection with the worm located within an intermediate portion of thehousing 6i), segments of the respective housing bodies are merged atright angles to each other, to form by a weld or braze at theirjunction, the integral structure best illustrated in FIG. 2. Moreparticularly, cylindrical sleeve 16 is received within an opening 80 ina cylindrical surface between the bearing portions 66 and 67 on thehousing 60. Supported for rotation within an extended, generallycylindrical cavity defined by the -inner .surface of housing 6i?, is anintegral shaft structure 72, comprising portions of varying lengths anddifferent diameters. Situated 0n this shaft structure between bearingsleeves 83 and 84, fitted upon reduced diameter end portions 81 and 82of the structure, is the worm 75, in proper position to operativelyengage the gear 2'7 attached to the cylinder 12. An input drive to theworm is received from a motor means 85 flexibility coupled by aconventional means 74 to a large 'diameter end portion 87 of the shaftstructure and transmitted to the worm through an extended intermediateshaft portion 86.

Since the `driven shaft structure 72 enters a potential high vacuum areaof the apparatus, two rotary O-ring seals 89 and 90 made of rubber, areapplied around the shaft portion 86 in the housing cavity 88. A seriesof adjustable compression sleeves 91, 92 and 93, securely tted aroundthe intermediate shaft portion 86, function to maintain the O-rings intheir proper place along the shaft, and in cooperation with anintermediate vacuum port 94, provide a vacuum tight seal between theatmosphere and the piston head end of the housing 15. A threadedconnection between an enlarged end 73 on the sleeve 93, and a threadedarea within housing cavity 88, permits this sleeve to be adjustedrelative to the housing and the shaft portion 86. By such means itbecomes possible to conviently apply pressure to the O: rings betweenthe several sleeves on the shaft portion 86, since the end sleeve 91 isheld from any displacement by its contact with xed bearing sleeve 83. Aslight over-compressed condition for the O-rings is needed initially inorder to have a proper contact between the O- rings and the metalsurface of the shaft therein, to obtain a vacuum seal. This follows fromthe fact that the rubber of the O-rings shrinks when subjected to thefrictional heat developed in them by the shaft structure rotating insuch rings. Therefore, the objective of adjusting sleeve 93 is toprecompress the O-rings just enough so subsequent shrinkage will leavethe rubber to metal contact vacuum tight but not so tight as to causeheating beyond an amount that would destroy the O-rings. Member 87 of'he drive shaft is supported in a set of bearings 96 set into acylindrical chamber 95 at the relatively large outer end of the housingcavity 88. The drive shaft extends beyond the vacuum seal and outsidethe housing 60, through a central opening in a threaded flange-likebushing element 97, which screws into the end rim of the housing toprovide a retaining member for the bearing elements 96. A conventionalthreaded plug 98 received within an opening in the housing wallimmediately beneath the worm 75, provides access thereto for lubricationas required.

Accurate measurement of the angle to which the assembled apparatus isinclined from the horizontal by means of gear members 68 and 70, isaccomplished by using a goniometer 101, set up alongside of one end ofthe apparatus. As best seen in FIG. 2, the goniometer cooperates with acircular glass plate 105 axially mounted on a stub end y106 of thehousing 60, and rotatable therewith about the axis B-B. Inscriptions onthei plate comprising gradiations of minutes of arc, are viewed througha stationary optical coincidence reading system 107 of the goniometer,lwherein a reading microscope and Vern-ier can be read directly to onesecond. This optical measuring instrument may have the form of onecommercially available as the UNISECj from W. & L. E. Gu-rley of Troy,New Jersey. Because plate 105 is fastened to stub 106 at an arbitrarysetting, and the position of the axis A-A through piston 10, withrespect to the base plate 61 cannot be determined independently, thegoniometer reading that corresponds ,to ythe true horizontal position ofthe piston is determined by bringing the piston into balance when thereis no pressure drop across it. As will be made more evident hereinafter,piston 4balance is indicated when the `thin edge of disk 39 is indexedabout the mid-point of scale 45.

Although the goniometer can be read very precisely, the accuracy withwhich the equilibrium angle of inclination can be measured dependsultimately on the `amount of friction produced on the relativelydisplaceable surfaces subject to contact bet-Ween the sleeve 16 and thecylinder 12, and the latter and piston 10. Frictional effects that werenot entirely removed by precision honing of the piston .and cylinder,are reducible to a negligible amount by an oscillatory movement impartedto the piston. Moreover, a relatively non-volatile vacuum pump oil isapplied to lubricate the critical piston, cylinder and sleeve surfaceswhereby a lubrication seal vis produced and remains effective at verylow pressures such that the pumping effect ordinarily observed on airlubricated piston-cylinder combinations, is eliminated. Lubricating withvacuum pump oil also allows the pressure measurements to be referred toa vacuum instead of an atmospheric datum level. As a result it ispossible to use `the present invention for measuring pressures as low as0.1 mm. Hg.

The present invention functions to bring about the aforementionedfriction defeating oscillatory movements without the use of any directmechanical Contact upon the piston. As a result, the equilibrium of thepiston is not distributed, or displaced with respect to the pressurebeing measured. Basically, the input for effecting the movements in thismanner is a rotational drive transmitted to the piston 10 from theconventional adjustable speed motor 85 .as shown in FIG. 2. Aspreviously indicated, suitable connections from the motor to the shaftstructure 72, causes the Worm 75 fixed thereto, to rotate gear 27 andthe cylinder 12 to which the gear is attached. Rotation of the cylinderat nearly constant speed in one direction in turn induces aunidirectional, rotational drive to Ithe piston 10 due to the drag inthe lubricating oil between the connecting surfaces of these parts. Disk39 rotating with the piston 10, consequently lowers and raises theweight 40 eccentrically mounted on the disk, and as a result thecontinuing variable forces engendered thereby are imposed on therotational drive, causing acceleration Ifollowed by de-acceleration inthe rotation of the piston and the parts attached thereto. In thismanner all critical frictional effects are substantially eliminated, andwithout producing thereby any net force along the axis of the piston.The oscillatory motion of the piston also eliminates the screw effectwhich would ordinarily occur when one part of the piston-cylindercombination is rotated continuously in one direction. As hereinaboveexplained, a highly efficient vacuum seal about the drive shaftstructure 72, is provided by the O-rings 89 and 90, in cooperation withsleeves 91, 92

and 93, to prevent pressure leakage into housing 15 during operation ofthe apparatus as described.

Utilization of the present invention for precision pressure measurementsrequires that the longitudinal axis B B through the housing 60, becarefully leveled to define a parallel reasonably close to thehorizontal. Any significant deviation of this axis from the horizontalwould interfere with any attempt to measure directly the angle yto whichhousing 15 is inclined to position the Weight of piston 10 forcounterbalancing the gas pressures. One method for accomplishing aproper leveling of the axis B-B of the housing 60, employs a telescopeattached along the top of housing enclosure |15, and a plumb line atwhich the telescope is sighted. The deviation angle can be reduced to afew minutes of arc by merely adjusting .the level of the base plate 61until the cross-lines on the telescope show no departure from alignmentwith the plumbliney when the housing is moved from the horizontal to afully inclined position. When housing 15 is angularly adjusted about anaccurately leveled axis to control its degree of inclination from thehorizontal, the effective weight to area ratio of its piston may beprecisely modified to assume any selected value within a predeterminedrange, including ze-ro when the housing is adjusted to a horizontalalignment.

To -obtain in accordance with the present invention, a measure-ment ofthe vapor pressure of a sample S shown in FIG. 3 as contained in ampoule2 suspended in a thermostat 3, requires that the vapors produced in theampoule be directed into a system of pipes and valves in the nature ofthat shown schematically in the figure. If the vapors of the sample areinert to the gauge parts, and the temperature of the sample is belowthat of the gauge and connecting lines, a valve 11 is opened and valve 8in a line 7, and a valve 9 on the ampoule, are closed while a line 4 andthe chambers 22 and 25 of the housing 15, are evacuated through a line 5.and valves 13 and 14, to a high vacuum up to l0-5 m-m. Hg. Gauging isbegun by closing valve 13, with valve 14 remaining open, so that a nullyreading can be taken on the goniometer with the piston in thehorizontal position. Upon completion of the null reading, with valve 13closed, the valve 9 is opened, allowing sample vapors to fill line 4 andchamber 22. The housing 15 is then tilted about the axis B-B shown inFIG. 2, by means of gears 68 and 70, such that the pressure forcesbuilt-up lby the vapors in chamber 22 become effective and tend todisplace piston 10 against the counter force of the pistons componentweight in the axial direction, since atmospheric pressure has beenremoved at the head end thereof. Tilting of housing 15 yabout the axisB-B is continued to incline the housing 15 from a horizontal -attitudetoward the angle 0, until indicator elements 39, 45, viewed in sightopening 44, sh-ow the reciprocating motion of the piston parallel to itslongitudinal axis A-A -is minimized at a minute degree of tilting. Uponarriving at this pressure equilibration between the piston and samplevapors, a final reading is taken on the goniometer. Valves 11 and 14remain open at all times during the pressure readmg.

An alternative operation for the system is necessary if the samplevapors are corrosive or the sample is at a temperature greater than thetemperature of any part of the gauge or line between the ampoule 2 andthe piston structure. In that case the sample S is isolated in thethermostat 3 by a sensitive, inert diaphragm of a pressure transducer 6,and nitrogen or some other suitable gas supplied through the pipe line7, is used to transmit the pressure from the diaphragm to the pistonchamber. To start, the operation is as previously described, with anevacuation of the gauge and lines, followed by the null reading on thegonimeter as was prescribed for the inert sample. However, in addition anull reading is obtained on the pressure transducer 6. Following the twonull readings, valves 13 and 11 are closed, and valve 9 is opened toallow nitrogen to bleed in (or out) through valve S to return thetransducer to the null point. Motion of the transducer diaphragm may beconveniently indicated on a capacitor meter 21. Since the diaphragm isdirectly subject to the vapor pressure in the ampoule 2, as well as thepistons counterbalancing force transmitted through the nitrogen in thelines, it functions to control indicator 21 in the same way as are theindicator elements 39 and 45 of the housing 15. The absolute value ofthe pressure of the nitrogen and therefore of the sample, can then beread on the piston gauge by a procedure wherein the smallest angularincrement in the over-all inclination of the housing and its piston isfound which will cause a reversal in `the direction of axial travel ofthe piston, and movement of the diaphragm back and forth an equal amounton each side of its null point. Since this pressure gauging requires anaxial movement of the piston, and consequently a change in the volume ofthe chamber 22 during gauging, the volume of nitrogen must be adjustedinitially to a value that will place the piston about midway in itsaxial travel when the transducer 6 is at a null indication. During thepressure reading in this instance, valves 9 and 14 remain open, whereasvalves 11 and 13 remain closed.

Thermostat 3 may be made according to any conventional construction forsuch an apparatus, although for the purposes of the present invention atemperature control in the neighborhood of 0.001 to 0.002 C. is needed.One suitable form of thermostat comprises an insulated cylindricalvessel, lled with liquid and provided with a stirrer, an electricalheater with manual adjustment, a smaller electrical heater having Iaprecise controller, and a cooling coil through which refrigerant can beflowed under temperature and rate control. Also within this thermostatis a temperature sensitive element comprising part of the temperaturecontroller, and a temperature measuring device such as a platinumresistance thermometer.

A basis for a theoretical relationship from which an absolute value ofthe vapor pressure Pmm, for the sample S, can be calculated, is found ina consideration of the opposing forces made to act on the piston 10 incarrying out the aforementioned procedures. A balance is achieved suchthat the component of the pistons weight along axis A-A is equal to thepressure force of the vapor upon the piston structure, and may be statedas g(W sin Pmm: gstd(A) which relates the pistons angle of inclinationfrom the horizontal 0, its effective area A and weight W, and the onsite and standard accelerations of gravity g and gsm.

The effective weight of the piston structure includes the weight of thecylindrical piston 10, the disk 39, and its supporting tube 38, theeccentrically mounted weight 40, and a small amount of lubricating oil.As required, additional weights such as element 48, may be placed insidethe hollow structure of piston 1i) to increase the pressure range. Forexample, when gold is used as a Weight the piston weight can beapproximately doubled. The amount of oil that contributes to the Weightof the piston can be assumed to be that which remained on the surface ofa properly lubricated piston as it was withdrawn from the cylinder. Theeffective area of the piston must also include a portion of thelubricating oil film. However, the thickness of the hlm becomes lessi-mportant as the diameter of the piston increases. For a one-inchpiston the arithmetical average diameter of the external diameter of thepiston and the internal diameter of the cylinder 12 can be used unlessan accuracy greater than l part in 10,000 is demanded.

Estimating the precision of the gauge proper is easily accomplishedsince the piston area and the weight are maintained constant, and theonly variable to be considered is therefore the angle of inclination 0.However,

in any over-all estimation of the precision and accuracy of a pressuremeasurement made by -means of the present invention, consideration mustalso be given to the operational characteristics of the variousancillary elements constituting the gauge arrangement. The nature andpurity of the sample, and the precision of the temperature control inthe sample thermostat 3, will each affect the inherent precision of avapor pressure measurement. Even though the vernier of the goniometercan be read to l second, the smallest practical increment in theinclination of the housing and piston that will reverse the direction ofits axial travel to find the minimum reciprocating displacement, isabout 5 seconds. Nevertheless, in terms of pressure, this increment isless than .0007 mm. Hg, on the average, whereby the resulting precisionachieved is better than one micron.

Because of the extremely precise measurements that can be made by meansof the present invention, it is applicable for determining vaporpressures below room temperature for high boiling or unstable organicsubstances that could not be stu-died by other known methods, as well asfor detonable or rare substances which require that their use be limitedto very small samples. From the data derived using the presentinvention, accurate values of heat and entropy of vaporization andentropy of compression can be calculated.

While a preferred embodiment of the invention has been illustrated anddescribed herein, it is to be understood that the invention is notlimited thereby, but is susceptible to changes in form and detail.

What is claimed is:

1. A precision pressure gauge comprising an elongated tubular shellenclosure, cylindrical chambers at the respective ends of the enclosureand an intermediate chamber therebetween, a cylindrical sleeve rotatablewithin said intermediate chamber of said enclosure, a cylindricalelement operatively maintained within a closely confining passage ofsaid cylindrical sleeve for linear and rotatable displacement thereinrelative to the longitudinal axis of said enclosure, said cylindricalelement having surfaces thereon facing said end chambers, separateconduit means providing a gaseous uid under pressure to one of said endchambers and removing gaseous fluid from `the other of said end chambersmeans supporting said enclosure for rotation about an axis transverse tosaid longitudinal axis thereof, said rotation causing the lineardisplacement of the said cylindrical element relative to said rotatablesleeve and said enclosure, a driving means in said supporting meansoperatively associated with means on said rotatable sleeve for rotatablydisplacing said sleeve and said cylindrical element about saidlongitudinal axis, said cylidrical element being rotated solely througha slipping contact connection with said rotatable sleeve, a diskattached to a rim of said cylindrical element comprising one of saidfacing surfaces, said disk being displaceable with said cylindricalelement in one of said end chambers, a weight xed to a peripheralportion of said disk being operatively effective when displaced withsaid disk upon rotational displacement of said cylindrical element toproduce an eccentrically directed force to modify the rotationaldisplacement of said cylindrical element, a sight opening in saidenclosure comprising an indexing element, said opening allowing a viewof said end chamber wherein the displacement of the disk upon lineardisplacement of the cylindrical element is seen in relation to theindexing element, said enclosure supporting means having mounted on anend portion thereof a plate rotatable therewith about a longitudinalaxis therethrough, said plate having angular indicia means thereon, andoptical means aligned with said indicia means facilitating viewing onsaid plate the angular displacements of said enclosure about saidtransverse axis thereof.

2. The pressure gauge of claim 1 wherein said enclosure supporting meanscomprises an elongated housing with which the said tubular shell of theenclosure is integrally combined to position the longitudinal axisthereof at right angles to that of said elongated housing, said drivingmeans in said support means comprising a shaft mounted for rotationabout said longitudinal taxis of the housing, and a gear on said shaftmeshing with a gear comprising said means on said cylindrical sleeve forrotatably displacing the said sleeve and the said element therein,further support means maintaining said elongated housing for rotationalbotut its longitudinal axis, further meshing gears connected to saidfurther support means and elongated housing to facilitate rotation ofthe latter about its longitudinal axis.

3. A precision gauge for measuring the pressure of a source thereof,comprising a first tubular housing formed as a plurality of contiguouschambers including a central chamber having operatively related thereinpiston and cylinder structures, means for connecting said cylinderstructure to said source, bearing devices supporting the said cylinderstructure for rotation about the longitudinal axis of the said iirsthousing, said piston structure being freely movable in said cylinderstructure for linear and rotative displacements therein on vacuum pumplubrication coating the mutually contacting surfaces of the piston andcylinder structures, a second tubular housing integrally joined with thesaid first housing, the respective longitudinal axes of the saidhousings being positioned thereby at right angles to each other, spacedsupport elements comprising bearing sleeves in which the said secondhousing is maintained for rotation about its longitudinal axis, drivenshaft means supported on bearing devices in said second housing forrotation about the said axis thereof, and having connected thereto meansimparting rotation to said cylinder structure in said first housing,drive means operatively associated with said support elementsand saidsecond housing to angularly position the latter about its said axis, andthe said axis of the first housing in a vertical plane, a plate mountedon an end portion of the said second housing to be rotatable therewithabout its said axis, and having graduated angular indicia on a facethereof, an optical coincidence reading system aligned with the saidplate face, and operable to read therefrom the angular displacement ofthe said axis of the lirst housing in a vertical plane.

4. The precision pressure gauge of claim 3, wherein said pistonstructure comprises a hollow elongated cylinder having an integralclosure portion at one end, and receiving in its open opposite end atubular element tightly tted therein, a disk concentrically attached tothe free end of the said tubular element and a weight fixed in aperipheral portion of said disk, whereby rotation of the cylinderstructure engenders a dragging force in said lubrication coating betweenthe piston and cylinder structures, such that a rotative force isimparted to the piston, and upon the angular displacement of thelongitudinal axis of the said rst housing on a vertical plane, a linearforce in an axial direction is superimposed on the said rotative forceimparted to the piston which additionally assumes an oscillatorymovement due to eccentric forces acting on the piston produced by theweight on said disk.

5. In a precision gauge for measuring the pressure of a source thereof,an elongated rst housing having vacuum tight sealing closures at itsopposite ends, and comprising Within a space between said closures arotatable sleeve, means for connecting said rotatable sleeve to saidsource, and a rotatable and displaceable piston operatively maintainedin said sleeve, a second housing integrally joined with said irsthousing at right angles thereto, an elongated cavity in said secondhousing and a passage from said cavity communicating with the :saidspace in the rst housing, a rotatable shaft structure spanning thelength of said cavity and extending outwardly from an end openingthereof, gear means operable in said passage having parts thereoffastened to said shaft structure in said cavity and to said rotatablesleeve whereby rotation of said shaft `drives said sleeve and the pistontherein, a vacuum seal means arranged to encircle a portion of saidshaft structure between said end opening in the cavity and the gearmeans, said seal means comprising two rubber O-rings respectivelysituated between a first and second sleeve and the latter and a thirdsleeve, said lirst sleeve being selectively adjustable within saidcavity to maintain said O-rings compressed between said sleeves, wherebythe O-rings are brought into pressured contact with said shaftstructure.

References Cited by the Examiner UNITED STATES PATENTS 5/ 1964 Lewis73-4 OTHER REFERENCES LOUIS R. PRINCE, Primary Examiner. DAVIDSCHONBERG, Examiner.

DONALD O. WOODIEL, Assistant Examiner.

3. A PRECISION GAUGE FOR MEASURING THE PRESSURE OF A SOURCE THEREOF,COMPRISING A FIRST TUBULAR HOUSING FORMED AS A PLURALITY OF CONTIGUOUSCHAMBERS INCLUDING A CENTRAL CHAMBER HAVING OPERATIVELY RELATED THEREINPISTON AND CYLINDER STRUCTURES, MEANS FOR CONNECTING SAID CYLINDERSTRUCTURE TO SAID SOURCE, BEARING DEVICES SUPPORTING THE SAID CYLINDERSTRUCTURE FOR ROTATION ABOUT THE LONGITUDINAL AXIS OF THE SAID FIRSTHOUSING, SAID PISTON STRUCTURE BEING FREELY MOVABLE IN SAID CYLINDERSTRUCTURE FOR LINEAR AND ROTATIVE DISPLACEMENTS THEREIN ON VACUUM PUMPLUBRICATION COATING THE MUTUALLY CONTACTING SURFACES OF THE PISTON ANDCYLINDER STRUCTURES, A SECOND TUBULAR HOUSING INTEGRALLY JOINED WITH THESAID FIRST HOUSING, THE RESPECTIVE LONGITUDINAL AXES OF THE SAIDHOUSINGS BEING POSITIONED THEREBY AT RIGHT ANGLES TO EACH OTHER, SPACEDSUPPORT ELEMENTS COMPRISING BEARING SLEEVES IN WHICH THE SAID SECONDHOUSING IS MAINTAINED FOR ROTATION ABOUT ITS LONGITUDINAL AXIS, DRIVENSHAFT MEANS SUPPORTED ON BEARING DEVICES IN SAID SECOND HOUSING FORROTATION ABOUT THE SAID AXIS THEREOF, AND HAVING CONNECTED THERETO MEANSIMPARTING ROTATION TO SAID CYLINDER STRUCTURE IN SAID FIRST HOUSING,DRIVE MEANS OPERATIVELY ASSOCIATED WITH SAID SUPPORT ELEMENTS AND SAIDSECOND HOUSING TO ANGULARLY POSITION THE LATTER ABOUT ITS SAID AXIS, ANDTHE SAID AXIS OF THE FIRST HOUSING IN A VERTICAL PLANE, A PLATE MOUNTEDON AN END PORTION OF THE SAID SECOND HOUSING TO BE ROTATABLE THEREWITHABOUT ITS SAID AXIS, AND HAVING GRADUATED ANGULAR INDICIA ON A FACETHEREOF, AN OPTICAL COINCIDENCE READING SYSTEM ALIGNED WITH THE SAIDPLATE FACE, AND OPERABLE TO READ THEREFROM THE ANGULAR DISPLACEMENT OFTHE SAID AXIS OF THE FIRST HOUSING IN A VERTICAL PLANE.